package org.mt4j.util;

import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.util.Collection;
import java.util.ConcurrentModificationException;
import java.util.Iterator;
import java.util.LinkedList;
import java.util.List;
import java.util.NoSuchElementException;
import java.util.Queue;
import java.util.Stack;

	/**
	 * Resizable-array implementation of the {@link Deque} interface.  Array
	 * deques have no capacity restrictions; they grow as necessary to support
	 * usage.  They are not thread-safe; in the absence of external
	 * synchronization, they do not support concurrent access by multiple threads.
	 * Null elements are prohibited.  This class is likely to be faster than
	 * {@link Stack} when used as a stack, and faster than {@link LinkedList}
	 * when used as a queue.
	 *
	 * <p>Most <tt>ArrayDeque</tt> operations run in amortized constant time.
	 * Exceptions include {@link #remove(Object) remove}, {@link
	 * #removeFirstOccurrence removeFirstOccurrence}, {@link #removeLastOccurrence
	 * removeLastOccurrence}, {@link #contains contains}, {@link #iterator
	 * iterator.remove()}, and the bulk operations, all of which run in linear
	 * time.
	 *
	 * <p>The iterators returned by this class's <tt>iterator</tt> method are
	 * <i>fail-fast</i>: If the deque is modified at any time after the iterator
	 * is created, in any way except through the iterator's own <tt>remove</tt>
	 * method, the iterator will generally throw a {@link
	 * ConcurrentModificationException}.  Thus, in the face of concurrent
	 * modification, the iterator fails quickly and cleanly, rather than risking
	 * arbitrary, non-deterministic behavior at an undetermined time in the
	 * future.
	 *
	 * <p>Note that the fail-fast behavior of an iterator cannot be guaranteed
	 * as it is, generally speaking, impossible to make any hard guarantees in the
	 * presence of unsynchronized concurrent modification.  Fail-fast iterators
	 * throw <tt>ConcurrentModificationException</tt> on a best-effort basis.
	 * Therefore, it would be wrong to write a program that depended on this
	 * exception for its correctness: <i>the fail-fast behavior of iterators
	 * should be used only to detect bugs.</i>
	 *
	 * <p>This class and its iterator implement all of the
	 * <em>optional</em> methods of the {@link Collection} and {@link
	 * Iterator} interfaces.
	 *
	 * <p>This class is a member of the
	 * <a href="{@docRoot}/../technotes/guides/collections/index.html">
	 * Java Collections Framework</a>.
	 *
	 * @author  Josh Bloch and Doug Lea
	 * @since   1.6
	 * @param <E> the type of elements held in this collection
	 */
	public class ArrayDeque<E>
	extends AbstractCollection<E>
//	                           implements Deque<E>, Cloneable, Serializable
	{
	    /**
	     * The array in which the elements of the deque are stored.
	     * The capacity of the deque is the length of this array, which is
	     * always a power of two. The array is never allowed to become
	     * full, except transiently within an addX method where it is
	     * resized (see doubleCapacity) immediately upon becoming full,
	     * thus avoiding head and tail wrapping around to equal each
	     * other.  We also guarantee that all array cells not holding
	     * deque elements are always null.
	     */
	    private transient E[] elements;

	    /**
	     * The index of the element at the head of the deque (which is the
	     * element that would be removed by remove() or pop()); or an
	     * arbitrary number equal to tail if the deque is empty.
	     */
	    private transient int head;

	    /**
	     * The index at which the next element would be added to the tail
	     * of the deque (via addLast(E), add(E), or push(E)).
	     */
	    private transient int tail;

	    /**
	     * The minimum capacity that we'll use for a newly created deque.
	     * Must be a power of 2.
	     */
	    private static final int MIN_INITIAL_CAPACITY = 8;

	    // ******  Array allocation and resizing utilities ******

	    /**
	     * Allocate empty array to hold the given number of elements.
	     *
	     * @param numElements  the number of elements to hold
	     */
	    private void allocateElements(int numElements) {
	        int initialCapacity = MIN_INITIAL_CAPACITY;
	        // Find the best power of two to hold elements.
	        // Tests "<=" because arrays aren't kept full.
	        if (numElements >= initialCapacity) {
	            initialCapacity = numElements;
	            initialCapacity |= (initialCapacity >>>  1);
	            initialCapacity |= (initialCapacity >>>  2);
	            initialCapacity |= (initialCapacity >>>  4);
	            initialCapacity |= (initialCapacity >>>  8);
	            initialCapacity |= (initialCapacity >>> 16);
	            initialCapacity++;

	            if (initialCapacity < 0)   // Too many elements, must back off
	                initialCapacity >>>= 1;// Good luck allocating 2 ^ 30 elements
	        }
	        elements = (E[]) new Object[initialCapacity];
	    }

	    /**
	     * Double the capacity of this deque.  Call only when full, i.e.,
	     * when head and tail have wrapped around to become equal.
	     */
	    private void doubleCapacity() {
	        assert head == tail;
	        int p = head;
	        int n = elements.length;
	        int r = n - p; // number of elements to the right of p
	        int newCapacity = n << 1;
	        if (newCapacity < 0)
	            throw new IllegalStateException("Sorry, deque too big");
	        Object[] a = new Object[newCapacity];
	        System.arraycopy(elements, p, a, 0, r);
	        System.arraycopy(elements, 0, a, r, p);
	        elements = (E[])a;
	        head = 0;
	        tail = n;
	    }

	    /**
	     * Copies the elements from our element array into the specified array,
	     * in order (from first to last element in the deque).  It is assumed
	     * that the array is large enough to hold all elements in the deque.
	     *
	     * @return its argument
	     */
	    private <T> T[] copyElements(T[] a) {
	        if (head < tail) {
	            System.arraycopy(elements, head, a, 0, size());
	        } else if (head > tail) {
	            int headPortionLen = elements.length - head;
	            System.arraycopy(elements, head, a, 0, headPortionLen);
	            System.arraycopy(elements, 0, a, headPortionLen, tail);
	        }
	        return a;
	    }

	    /**
	     * Constructs an empty array deque with an initial capacity
	     * sufficient to hold 16 elements.
	     */
	    public ArrayDeque() {
	        elements = (E[]) new Object[16];
	    }

	    /**
	     * Constructs an empty array deque with an initial capacity
	     * sufficient to hold the specified number of elements.
	     *
	     * @param numElements  lower bound on initial capacity of the deque
	     */
	    public ArrayDeque(int numElements) {
	        allocateElements(numElements);
	    }

	    /**
	     * Constructs a deque containing the elements of the specified
	     * collection, in the order they are returned by the collection's
	     * iterator.  (The first element returned by the collection's
	     * iterator becomes the first element, or <i>front</i> of the
	     * deque.)
	     *
	     * @param c the collection whose elements are to be placed into the deque
	     * @throws NullPointerException if the specified collection is null
	     */
	    public ArrayDeque(Collection<? extends E> c) {
	        allocateElements(c.size());
	        addAll(c);
	    }

	    // The main insertion and extraction methods are addFirst,
	    // addLast, pollFirst, pollLast. The other methods are defined in
	    // terms of these.

	    /**
	     * Inserts the specified element at the front of this deque.
	     *
	     * @param e the element to add
	     * @throws NullPointerException if the specified element is null
	     */
	    public void addFirst(E e) {
	        if (e == null)
	            throw new NullPointerException();
	        elements[head = (head - 1) & (elements.length - 1)] = e;
	        if (head == tail)
	            doubleCapacity();
	    }

	    /**
	     * Inserts the specified element at the end of this deque.
	     *
	     * <p>This method is equivalent to {@link #add}.
	     *
	     * @param e the element to add
	     * @throws NullPointerException if the specified element is null
	     */
	    public void addLast(E e) {
	        if (e == null)
	            throw new NullPointerException();
	        elements[tail] = e;
	        if ( (tail = (tail + 1) & (elements.length - 1)) == head)
	            doubleCapacity();
	    }

	    /**
	     * Inserts the specified element at the front of this deque.
	     *
	     * @param e the element to add
	     * @return <tt>true</tt> (as specified by {@link Deque#offerFirst})
	     * @throws NullPointerException if the specified element is null
	     */
	    public boolean offerFirst(E e) {
	        addFirst(e);
	        return true;
	    }

	    /**
	     * Inserts the specified element at the end of this deque.
	     *
	     * @param e the element to add
	     * @return <tt>true</tt> (as specified by {@link Deque#offerLast})
	     * @throws NullPointerException if the specified element is null
	     */
	    public boolean offerLast(E e) {
	        addLast(e);
	        return true;
	    }

	    /**
	     * @throws NoSuchElementException {@inheritDoc}
	     */
	    public E removeFirst() {
	        E x = pollFirst();
	        if (x == null)
	            throw new NoSuchElementException();
	        return x;
	    }

	    /**
	     * @throws NoSuchElementException {@inheritDoc}
	     */
	    public E removeLast() {
	        E x = pollLast();
	        if (x == null)
	            throw new NoSuchElementException();
	        return x;
	    }

	    public E pollFirst() {
	        int h = head;
	        E result = elements[h]; // Element is null if deque empty
	        if (result == null)
	            return null;
	        elements[h] = null;     // Must null out slot
	        head = (h + 1) & (elements.length - 1);
	        return result;
	    }

	    public E pollLast() {
	        int t = (tail - 1) & (elements.length - 1);
	        E result = elements[t];
	        if (result == null)
	            return null;
	        elements[t] = null;
	        tail = t;
	        return result;
	    }

	    /**
	     * @throws NoSuchElementException {@inheritDoc}
	     */
	    public E getFirst() {
	        E x = elements[head];
	        if (x == null)
	            throw new NoSuchElementException();
	        return x;
	    }

	    /**
	     * @throws NoSuchElementException {@inheritDoc}
	     */
	    public E getLast() {
	        E x = elements[(tail - 1) & (elements.length - 1)];
	        if (x == null)
	            throw new NoSuchElementException();
	        return x;
	    }

	    public E peekFirst() {
	        return elements[head]; // elements[head] is null if deque empty
	    }

	    public E peekLast() {
	        return elements[(tail - 1) & (elements.length - 1)];
	    }

	    /**
	     * Removes the first occurrence of the specified element in this
	     * deque (when traversing the deque from head to tail).
	     * If the deque does not contain the element, it is unchanged.
	     * More formally, removes the first element <tt>e</tt> such that
	     * <tt>o.equals(e)</tt> (if such an element exists).
	     * Returns <tt>true</tt> if this deque contained the specified element
	     * (or equivalently, if this deque changed as a result of the call).
	     *
	     * @param o element to be removed from this deque, if present
	     * @return <tt>true</tt> if the deque contained the specified element
	     */
	    public boolean removeFirstOccurrence(Object o) {
	        if (o == null)
	            return false;
	        int mask = elements.length - 1;
	        int i = head;
	        E x;
	        while ( (x = elements[i]) != null) {
	            if (o.equals(x)) {
	                delete(i);
	                return true;
	            }
	            i = (i + 1) & mask;
	        }
	        return false;
	    }

	    /**
	     * Removes the last occurrence of the specified element in this
	     * deque (when traversing the deque from head to tail).
	     * If the deque does not contain the element, it is unchanged.
	     * More formally, removes the last element <tt>e</tt> such that
	     * <tt>o.equals(e)</tt> (if such an element exists).
	     * Returns <tt>true</tt> if this deque contained the specified element
	     * (or equivalently, if this deque changed as a result of the call).
	     *
	     * @param o element to be removed from this deque, if present
	     * @return <tt>true</tt> if the deque contained the specified element
	     */
	    public boolean removeLastOccurrence(Object o) {
	        if (o == null)
	            return false;
	        int mask = elements.length - 1;
	        int i = (tail - 1) & mask;
	        E x;
	        while ( (x = elements[i]) != null) {
	            if (o.equals(x)) {
	                delete(i);
	                return true;
	            }
	            i = (i - 1) & mask;
	        }
	        return false;
	    }

	    // *** Queue methods ***

	    /**
	     * Inserts the specified element at the end of this deque.
	     *
	     * <p>This method is equivalent to {@link #addLast}.
	     *
	     * @param e the element to add
	     * @return <tt>true</tt> (as specified by {@link Collection#add})
	     * @throws NullPointerException if the specified element is null
	     */
	    public boolean add(E e) {
	        addLast(e);
	        return true;
	    }

	    /**
	     * Inserts the specified element at the end of this deque.
	     *
	     * <p>This method is equivalent to {@link #offerLast}.
	     *
	     * @param e the element to add
	     * @return <tt>true</tt> (as specified by {@link Queue#offer})
	     * @throws NullPointerException if the specified element is null
	     */
	    public boolean offer(E e) {
	        return offerLast(e);
	    }

	    /**
	     * Retrieves and removes the head of the queue represented by this deque.
	     *
	     * This method differs from {@link #poll poll} only in that it throws an
	     * exception if this deque is empty.
	     *
	     * <p>This method is equivalent to {@link #removeFirst}.
	     *
	     * @return the head of the queue represented by this deque
	     * @throws NoSuchElementException {@inheritDoc}
	     */
	    public E remove() {
	        return removeFirst();
	    }

	    /**
	     * Retrieves and removes the head of the queue represented by this deque
	     * (in other words, the first element of this deque), or returns
	     * <tt>null</tt> if this deque is empty.
	     *
	     * <p>This method is equivalent to {@link #pollFirst}.
	     *
	     * @return the head of the queue represented by this deque, or
	     *         <tt>null</tt> if this deque is empty
	     */
	    public E poll() {
	        return pollFirst();
	    }

	    /**
	     * Retrieves, but does not remove, the head of the queue represented by
	     * this deque.  This method differs from {@link #peek peek} only in
	     * that it throws an exception if this deque is empty.
	     *
	     * <p>This method is equivalent to {@link #getFirst}.
	     *
	     * @return the head of the queue represented by this deque
	     * @throws NoSuchElementException {@inheritDoc}
	     */
	    public E element() {
	        return getFirst();
	    }

	    /**
	     * Retrieves, but does not remove, the head of the queue represented by
	     * this deque, or returns <tt>null</tt> if this deque is empty.
	     *
	     * <p>This method is equivalent to {@link #peekFirst}.
	     *
	     * @return the head of the queue represented by this deque, or
	     *         <tt>null</tt> if this deque is empty
	     */
	    public E peek() {
	        return peekFirst();
	    }

	    // *** Stack methods ***

	    /**
	     * Pushes an element onto the stack represented by this deque.  In other
	     * words, inserts the element at the front of this deque.
	     *
	     * <p>This method is equivalent to {@link #addFirst}.
	     *
	     * @param e the element to push
	     * @throws NullPointerException if the specified element is null
	     */
	    public void push(E e) {
	        addFirst(e);
	    }

	    /**
	     * Pops an element from the stack represented by this deque.  In other
	     * words, removes and returns the first element of this deque.
	     *
	     * <p>This method is equivalent to {@link #removeFirst()}.
	     *
	     * @return the element at the front of this deque (which is the top
	     *         of the stack represented by this deque)
	     * @throws NoSuchElementException {@inheritDoc}
	     */
	    public E pop() {
	        return removeFirst();
	    }

	    private void checkInvariants() {
		assert elements[tail] == null;
		assert head == tail ? elements[head] == null :
		    (elements[head] != null &&
		     elements[(tail - 1) & (elements.length - 1)] != null);
		assert elements[(head - 1) & (elements.length - 1)] == null;
	    }

	    /**
	     * Removes the element at the specified position in the elements array,
	     * adjusting head and tail as necessary.  This can result in motion of
	     * elements backwards or forwards in the array.
	     *
	     * <p>This method is called delete rather than remove to emphasize
	     * that its semantics differ from those of {@link List#remove(int)}.
	     *
	     * @return true if elements moved backwards
	     */
	    private boolean delete(int i) {
	 	checkInvariants();
		final E[] elements = this.elements;
		final int mask = elements.length - 1;
		final int h = head;
		final int t = tail;
		final int front = (i - h) & mask;
		final int back  = (t - i) & mask;

		// Invariant: head <= i < tail mod circularity
		if (front >= ((t - h) & mask))
		    throw new ConcurrentModificationException();

		// Optimize for least element motion
		if (front < back) {
		    if (h <= i) {
			System.arraycopy(elements, h, elements, h + 1, front);
		    } else { // Wrap around
			System.arraycopy(elements, 0, elements, 1, i);
			elements[0] = elements[mask];
			System.arraycopy(elements, h, elements, h + 1, mask - h);
		    }
		    elements[h] = null;
		    head = (h + 1) & mask;
		    return false;
		} else {
		    if (i < t) { // Copy the null tail as well
			System.arraycopy(elements, i + 1, elements, i, back);
			tail = t - 1;
		    } else { // Wrap around
			System.arraycopy(elements, i + 1, elements, i, mask - i);
			elements[mask] = elements[0];
			System.arraycopy(elements, 1, elements, 0, t);
			tail = (t - 1) & mask;
		    }
		    return true;
		}
	    }

	    // *** Collection Methods ***

	    /**
	     * Returns the number of elements in this deque.
	     *
	     * @return the number of elements in this deque
	     */
	    public int size() {
	        return (tail - head) & (elements.length - 1);
	    }

	    /**
	     * Returns <tt>true</tt> if this deque contains no elements.
	     *
	     * @return <tt>true</tt> if this deque contains no elements
	     */
	    public boolean isEmpty() {
	        return head == tail;
	    }

	    /**
	     * Returns an iterator over the elements in this deque.  The elements
	     * will be ordered from first (head) to last (tail).  This is the same
	     * order that elements would be dequeued (via successive calls to
	     * {@link #remove} or popped (via successive calls to {@link #pop}).
	     *
	     * @return an iterator over the elements in this deque
	     */
	    public Iterator<E> iterator() {
	        return new DeqIterator();
	    }

	    public Iterator<E> descendingIterator() {
	        return new DescendingIterator();
	    }

	    private class DeqIterator implements Iterator<E> {
	        /**
	         * Index of element to be returned by subsequent call to next.
	         */
	        private int cursor = head;

	        /**
	         * Tail recorded at construction (also in remove), to stop
	         * iterator and also to check for comodification.
	         */
	        private int fence = tail;

	        /**
	         * Index of element returned by most recent call to next.
	         * Reset to -1 if element is deleted by a call to remove.
	         */
	        private int lastRet = -1;

	        public boolean hasNext() {
	            return cursor != fence;
	        }

	        public E next() {
	            if (cursor == fence)
	                throw new NoSuchElementException();
	            E result = elements[cursor];
	            // This check doesn't catch all possible comodifications,
	            // but does catch the ones that corrupt traversal
	            if (tail != fence || result == null)
	                throw new ConcurrentModificationException();
	            lastRet = cursor;
	            cursor = (cursor + 1) & (elements.length - 1);
	            return result;
	        }

	        public void remove() {
	            if (lastRet < 0)
	                throw new IllegalStateException();
	            if (delete(lastRet)) { // if left-shifted, undo increment in next()
	                cursor = (cursor - 1) & (elements.length - 1);
			fence = tail;
		    }
	            lastRet = -1;
	        }
	    }

	    private class DescendingIterator implements Iterator<E> {
	        /*
	         * This class is nearly a mirror-image of DeqIterator, using
	         * tail instead of head for initial cursor, and head instead of
	         * tail for fence.
	         */
	        private int cursor = tail;
	        private int fence = head;
	        private int lastRet = -1;

	        public boolean hasNext() {
	            return cursor != fence;
	        }

	        public E next() {
	            if (cursor == fence)
	                throw new NoSuchElementException();
	            cursor = (cursor - 1) & (elements.length - 1);
		    E result = elements[cursor];
	            if (head != fence || result == null)
	                throw new ConcurrentModificationException();
	            lastRet = cursor;
	            return result;
	        }

	        public void remove() {
	            if (lastRet < 0)
	                throw new IllegalStateException();
	            if (!delete(lastRet)) {
	                cursor = (cursor + 1) & (elements.length - 1);
			fence = head;
		    }
	            lastRet = -1;
	        }
	    }

	    /**
	     * Returns <tt>true</tt> if this deque contains the specified element.
	     * More formally, returns <tt>true</tt> if and only if this deque contains
	     * at least one element <tt>e</tt> such that <tt>o.equals(e)</tt>.
	     *
	     * @param o object to be checked for containment in this deque
	     * @return <tt>true</tt> if this deque contains the specified element
	     */
	    public boolean contains(Object o) {
	        if (o == null)
	            return false;
	        int mask = elements.length - 1;
	        int i = head;
	        E x;
	        while ( (x = elements[i]) != null) {
	            if (o.equals(x))
	                return true;
	            i = (i + 1) & mask;
	        }
	        return false;
	    }

	    /**
	     * Removes a single instance of the specified element from this deque.
	     * If the deque does not contain the element, it is unchanged.
	     * More formally, removes the first element <tt>e</tt> such that
	     * <tt>o.equals(e)</tt> (if such an element exists).
	     * Returns <tt>true</tt> if this deque contained the specified element
	     * (or equivalently, if this deque changed as a result of the call).
	     *
	     * <p>This method is equivalent to {@link #removeFirstOccurrence}.
	     *
	     * @param o element to be removed from this deque, if present
	     * @return <tt>true</tt> if this deque contained the specified element
	     */
	    public boolean remove(Object o) {
	        return removeFirstOccurrence(o);
	    }

	    /**
	     * Removes all of the elements from this deque.
	     * The deque will be empty after this call returns.
	     */
	    public void clear() {
	        int h = head;
	        int t = tail;
	        if (h != t) { // clear all cells
	            head = tail = 0;
	            int i = h;
	            int mask = elements.length - 1;
	            do {
	                elements[i] = null;
	                i = (i + 1) & mask;
	            } while (i != t);
	        }
	    }

	    /**
	     * Returns an array containing all of the elements in this deque
	     * in proper sequence (from first to last element).
	     *
	     * <p>The returned array will be "safe" in that no references to it are
	     * maintained by this deque.  (In other words, this method must allocate
	     * a new array).  The caller is thus free to modify the returned array.
	     *
	     * <p>This method acts as bridge between array-based and collection-based
	     * APIs.
	     *
	     * @return an array containing all of the elements in this deque
	     */
	    public Object[] toArray() {
		return copyElements(new Object[size()]);
	    }

	    /**
	     * Returns an array containing all of the elements in this deque in
	     * proper sequence (from first to last element); the runtime type of the
	     * returned array is that of the specified array.  If the deque fits in
	     * the specified array, it is returned therein.  Otherwise, a new array
	     * is allocated with the runtime type of the specified array and the
	     * size of this deque.
	     *
	     * <p>If this deque fits in the specified array with room to spare
	     * (i.e., the array has more elements than this deque), the element in
	     * the array immediately following the end of the deque is set to
	     * <tt>null</tt>.
	     *
	     * <p>Like the {@link #toArray()} method, this method acts as bridge between
	     * array-based and collection-based APIs.  Further, this method allows
	     * precise control over the runtime type of the output array, and may,
	     * under certain circumstances, be used to save allocation costs.
	     *
	     * <p>Suppose <tt>x</tt> is a deque known to contain only strings.
	     * The following code can be used to dump the deque into a newly
	     * allocated array of <tt>String</tt>:
	     *
	     * <pre>
	     *     String[] y = x.toArray(new String[0]);</pre>
	     *
	     * Note that <tt>toArray(new Object[0])</tt> is identical in function to
	     * <tt>toArray()</tt>.
	     *
	     * @param a the array into which the elements of the deque are to
	     *          be stored, if it is big enough; otherwise, a new array of the
	     *          same runtime type is allocated for this purpose
	     * @return an array containing all of the elements in this deque
	     * @throws ArrayStoreException if the runtime type of the specified array
	     *         is not a supertype of the runtime type of every element in
	     *         this deque
	     * @throws NullPointerException if the specified array is null
	     */
	    public <T> T[] toArray(T[] a) {
	        int size = size();
	        if (a.length < size)
	            a = (T[])java.lang.reflect.Array.newInstance(
	                    a.getClass().getComponentType(), size);
		copyElements(a);
	        if (a.length > size)
	            a[size] = null;
	        return a;
	    }

	    // *** Object methods ***

	    /**
	     * Returns a copy of this deque.
	     *
	     * @return a copy of this deque
	     */
	    public ArrayDeque<E> clone() {
	        try {
	            ArrayDeque<E> result = (ArrayDeque<E>) super.clone();
	            // Classpath local: we don't have Arrays.copyOf yet.
	            // result.elements = Arrays.copyOf(elements, elements.length);
	            result.elements = elements.clone();
	            return result;

	        } catch (CloneNotSupportedException e) {
	            throw new AssertionError();
	        }
	    }

	    /**
	     * Appease the serialization gods.
	     */
	    private static final long serialVersionUID = 2340985798034038923L;

	    /**
	     * Serialize this deque.
	     *
	     * @serialData The current size (<tt>int</tt>) of the deque,
	     * followed by all of its elements (each an object reference) in
	     * first-to-last order.
	     */
	    private void writeObject(ObjectOutputStream s) throws IOException {
	        s.defaultWriteObject();

	        // Write out size
	        s.writeInt(size());

	        // Write out elements in order.
	        int mask = elements.length - 1;
	        for (int i = head; i != tail; i = (i + 1) & mask)
	            s.writeObject(elements[i]);
	    }

	    /**
	     * Deserialize this deque.
	     */
	    private void readObject(ObjectInputStream s)
	            throws IOException, ClassNotFoundException {
	        s.defaultReadObject();

	        // Read in size and allocate array
	        int size = s.readInt();
	        allocateElements(size);
	        head = 0;
	        tail = size;

	        // Read in all elements in the proper order.
	        for (int i = 0; i < size; i++)
	            elements[i] = (E)s.readObject();
	    }
	}
